Needle loss in subclavian vein during central venous catheter placement: case report of a rare complication.

We present a case of needle separation during central venous catheter (CVC) placement in a super morbidly obese patient with subsequent surgical intervention in its retrieval. This complication, potentially lethal due to the relevant anatomy of such a procedure, alerts critical care physicians and surgeons to the possibility of equipment failure and stresses proper technique in what has become a routine procedure. It also emphasizes the routine use of ultrasound-guidance for cannulation in patients of any body habitus. While infection and arrhythmia are the generally known complications of CVC placement, clinicians must be alert to unanticipated events such as needle separation. In our case, the retrieval of this needle required multi-disciplinary intervention between radiology, critical care, vascular surgery, and thoracic surgery. Our event stresses hypervigilance to complications in a common procedure.

Elevated hepatic fatty acid elongase-5 activity affects multiple pathways controlling hepatic lipid and carbohydrate composition.

Hepatic fatty acid elongase-5 (Elovl-5) plays an important role in long chain monounsaturated and polyunsaturated fatty acid synthesis. Elovl-5 activity is regulated during development, by diet, hormones, and drugs, and in chronic disease. This report examines the impact of elevated Elovl-5 activity on hepatic function. Adenovirus-mediated induction of Elovl5 activity in livers of C57BL/6 mice increased hepatic and plasma levels of dihomo-gamma-linolenic acid (20:3,n-6) while suppressing hepatic arachidonic acid (20:4,n-6) and docosahexaenoic acid (22:6,n-3) content. The fasting-refeeding response of peroxisome proliferator-activated receptor alpha-regulated genes was attenuated in mice with elevated Elovl5 activity. In contrast, the fasting-refeeding response of hepatic sterol-regulatory element binding protein-1 (SREBP-1)-regulated and carbohydrate-regulatory element binding protein/Max-like factor X-regulated genes, Akt and glycogen synthase kinase (Gsk)-3beta phosphorylation, and the accumulation of hepatic glycogen content and nuclear SREBP-1 were not impaired by elevated Elovl5 activity. Hepatic triglyceride content and the phosphorylation of AMP-activated kinase alpha and Jun kinase 1/2 were reduced by elevated Elovl5 activity. Hepatic phosphoenolpyruvate carboxykinase expression was suppressed, while hepatic glycogen content and phosphorylated Gsk-3beta were significantly increased, in livers of fasted mice with increased Elovl5 activity. As such, hepatic Elovl5 activity may affect hepatic glucose production during fasting. In summary, Elovl5-induced changes in hepatic fatty acid content affect multiple pathways regulating hepatic lipid and carbohydrate composition.

Docosahexaenoic acid (DHA) and hepatic gene transcription.

The type and quantity of dietary fat ingested contributes to the onset and progression of chronic diseases, like diabetes and atherosclerosis. The liver plays a central role in whole body lipid metabolism and responds rapidly to changes in dietary fat composition. Polyunsaturated fatty acids (PUFA) play a key role in membrane composition and function, metabolism and the control of gene expression. Certain PUFA, like the n-3 PUFA, enhance hepatic fatty acid oxidation and inhibit fatty acid synthesis and VLDL secretion, in part, by regulating gene expression. Our studies have established that key transcription factors, like PPARalpha, SREBP-1, ChREBP and MLX, are regulated by n-3 PUFA, which in turn control levels of proteins involved in lipid and carbohydrate metabolism. Of the n-3 PUFA, 22:6,n-3 has recently been established as a key controller of hepatic lipid synthesis. 22:6,n-3 controls the 26S proteasomal degradation of the nuclear form of SREBP-1. SREBP-1 is a major transcription factor that controls the expression of multiple genes involved fatty acid synthesis and desaturation. 22:6,n-3 suppresses nuclear SREBP-1, which in turn suppresses lipogenesis. This mechanism is achieved, in part, through control of the phosphorylation status of protein kinases. This review will examine both the general features of PUFA-regulated hepatic gene transcription and highlight the unique mechanisms by which 22:6,n-3 impacts gene expression. The outcome of this analysis will reveal that changes in hepatic 22:6,n-3 content has a major impact on hepatic lipid and carbohydrate metabolism. Moreover, the mechanisms involve 22:6,n-3 control of several well-known signaling pathways, such as Akt, Erk1/2, Gsk3beta and PKC (novel or atypical). 22:6,n-3 control of these same signaling pathways in non-hepatic tissues may help to explain the diverse actions of n-3 PUFA on such complex physiological processes as visual acuity and learning.

Regulation of hepatic fatty acid elongase and desaturase expression in diabetes and obesity.

Fatty acid elongases and desaturases play an important role in hepatic and whole body lipid composition. We examined the role that key transcription factors played in the control of hepatic elongase and desaturase expression. Studies with peroxisome proliferator-activated receptor alpha (PPARalpha)-deficient mice establish that PPARalpha was required for WY14643-mediated induction of fatty acid elongase-5 (Elovl-5), Elovl-6, and all three desaturases [Delta(5) desaturase (Delta(5)D), Delta(6)D, and Delta(9)D]. Increased nuclear sterol-regulatory element binding protein-1 (SREBP-1) correlated with enhanced expression of Elovl-6, Delta(5)D, Delta(6)D, and Delta(9)D. Only Delta(9)D was also regulated independently by liver X receptor (LXR) agonist. Glucose induction of l-type pyruvate kinase, Delta(9)D, and Elovl-6 expression required the carbohydrate-regulatory element binding protein/MAX-like factor X (ChREBP/MLX) heterodimer. Suppression of Elovl-6 and Delta(9)D expression in livers of streptozotocin-induced diabetic rats and high fat-fed glucose-intolerant mice correlated with low levels of nuclear SREBP-1. In leptin-deficient obese mice (Lep(ob/ob)), increased SREBP-1 and MLX nuclear content correlated with the induction of Elovl-5, Elovl-6, and Delta(9)D expression and the massive accumulation of monounsaturated fatty acids (18:1,n-7 and 18:1,n-9) in neutral lipids. Diabetes- and obesity-induced changes in hepatic lipid composition correlated with changes in elongase and desaturase expression. In conclusion, these studies establish a role for PPARalpha, LXR, SREBP-1, ChREBP, and MLX in the control of hepatic fatty acid elongase and desaturase expression and lipid composition.

Docosahexaneoic acid (22:6,n-3) regulates rat hepatocyte SREBP-1 nuclear abundance by Erk- and 26S proteasome-dependent pathways.

Insulin induces and dietary n-3 PUFAs suppress hepatic de novo lipogenesis by controlling sterol-regulatory element binding protein-1 nuclear abundance (nSREBP-1). Our goal was to define the mechanisms involved in this regulatory process. Insulin treatment of rat primary hepatocytes rapidly augments nSREBP-1 and mRNA(SREBP-1c) while suppressing mRNA(Insig-2) but not mRNA(Insig-1). These events are preceded by rapid but transient increases in Akt and Erk phosphorylation. Removal of insulin from hepatocytes leads to a rapid decline in nSREBP-1 [half-time (T1/2) approximately 10 h] that is abrogated by inhibitors of 26S proteasomal degradation. 22:6,n-3, the major n-3 PUFA accumulating in livers of fish oil-fed rats, suppresses hepatocyte levels of nSREBP-1, mRNA(SREBP-1c), and mRNA(Insig-2) but modestly and transiently induces mRNA(Insig-1). More importantly, 22:6,n-3 accelerates the disappearance of hepatocyte nSREBP-1 (T1/2 approximately 4 h) through a 26S proteasome-dependent process. 22:6,n-3 has minimal effects on microsomal SREBP-1 and sterol-regulatory element binding protein cleavage-activating protein or nuclear SREBP-2. 22:6,n-3 transiently inhibits insulin-induced Akt phosphorylation but induces Erk phosphorylation. Inhibitors of Erk phosphorylation, but not overexpressed constitutively active Akt, rapidly attenuate 22:6,n-3 suppression of nSREBP-1. Thus, 22:6,n-3 suppresses hepatocyte nSREBP-1 through 26S proteasome- and Erk-dependent pathways. These studies reveal a novel mechanism for n-3 PUFA regulation of hepatocyte nSREBP-1 and lipid metabolism.

Fatty acid regulation of hepatic gene transcription.

Dietary fat regulates gene expression by controlling the activity or abundance of key transcription factors. In vitro binding and cell culture studies have identified many transcription factors as prospective targets for fatty acid regulation, including peroxisome proliferator-activated receptors (PPARalpha, beta, gamma1, and gamma2), sterol regulatory element binding protein-1c (SREBP-1c), hepatic nuclear factors (HNF-4alpha and gamma), retinoid X receptor (RXRalpha), liver X receptor (LXRalpha), and others. In vivo studies established that PPARalpha- and SREBP-1c-regulated genes are key targets for PUFA control of hepatic gene expression. PUFA activate PPARalpha by direct binding, leading to the induction of hepatic fatty acid oxidation. PUFA inhibit hepatic fatty acid synthesis by suppressing SREBP-1c nuclear abundance through several mechanisms, including suppression of SREBP-1c gene transcription and enhancement of proteasomal degradation and mRNA(SREBP1c) decay. Changes in intracellular nonesterified fatty acids (NEFA) correlate well with changes in PPARalpha activity and mRNA(SREBP-1c) abundance. Several mechanisms regulate intracellular NEFA composition, including fatty acid transport, acyl CoA synthetases and thioesterases, fatty acid elongases and desaturases, neutral and polar lipid lipases, and fatty acid oxidation. Many of these mechanisms are regulated by PPARalpha or SREBP-1c. Together, these mechanisms control hepatic lipid composition and affect whole-body lipid composition.

Tissue-specific, nutritional, and developmental regulation of rat fatty acid elongases.

Of the six fatty acid elongase (Elovl) subtypes expressed in mammals, adult rat liver expresses four subtypes: Elovl-5 > Elovl-1 = Elovl-2 = Elovl-6. Overnight starvation and fish oil-enriched diets repressed hepatic elongase activity in livers of adult male rats. Diet-induced changes in elongase activity correlate with Elovl-5 and Elovl-6 mRNA abundance. Adult rats fed the peroxisome proliferator-activated receptor alpha (PPARalpha) agonist WY14,643 have increased hepatic elongase activity, Elovl-1, Elovl-5, Elovl-6, Delta5, Delta6, and Delta9 desaturase mRNA abundance, and mead acid (20:3,n-9) content. PPARalpha agonists affect both fatty acid elongation and desaturation pathways leading to changes in hepatic lipid composition. Elovl activity is low in fetal liver but increases significantly after birth. Developmental changes in hepatic elongase activity paralleled the postnatal induction of Elovl-5 mRNA and mRNAs encoding the PPARalpha-regulated transcripts, Delta5 and Delta6 desaturase, and cytochrome P450 4A. In contrast, Elovl-6, Delta9 desaturase, and FAS mRNA abundance paralleled changes in hepatic sterol regulatory element binding protein 1c (SREBP-1c) nuclear content. SREBP-1c is present in fetal liver nuclei, absent from nuclei immediately after birth, and reappears in nuclei at weaning, 21 days postpartum. In conclusion, changes in Elovl-5 expression may account for much of the nutritional and developmental control of fatty acid elongation activity in the rat liver.

The role of liver X receptor-alpha in the fatty acid regulation of hepatic gene expression.

Liver X receptors (LXR) alpha and beta play an important role in regulating the expression of genes involved in hepatic bile and fatty acid synthesis, glucose metabolism, as well as sterol efflux. Studies with human embryonic kidney 293 cells indicate that unsaturated fatty acids interfere with oxysterols binding to LXR and antagonize oxysterol-induced LXRalpha activity. In this report, we evaluated the effects of unsaturated fatty acids on LXR-regulated hepatic gene expression. The LXR agonist, T1317, induced mRNAs encoding sterol regulatory element-binding protein 1c (SREBP-1c) and two SREBP-1c-regulated lipogenic genes, e.g. fatty-acid synthase and the S14 protein in primary hepatocytes. Treatment of hepatocytes with eicosapentaenoic acid (20:5n-3) suppressed these mRNAs in the absence and presence of T1317. The cis-regulatory elements targeted by T1317 were not required for fatty-acid suppression of FAS or S14 promoter activity. In contrast to SREBP-1-regulated lipogenic genes, 20:5n-3 had no effect on the T1317 induction of ABCG5 or ABCG8 in the rat hepatoma cell line, FTO-2B. These two genes require LXR but not SREBP-1c for their expression. Feeding rats a diet supplemented with fish oil suppressed hepatic SREBP-1c-regulated genes and induced PPARalpha-regulated genes but had no effect on the LXR-regulated transcripts, CYP7A1, ABCG5, or ABCG8. Transfection studies, using either full-length hLXRalpha or a chimera containing only the LXRalpha ligand binding domain, indicate that a wide array of unsaturated fatty acids had little effect on LXRalpha activity in primary hepatocytes or FTO-2B. These studies suggest that LXRalpha is not a target for unsaturated fatty acid regulation in primary rat hepatocytes or in liver. Thus, oxysterol/LXR-mediated regulation of transcripts involved in bile acid synthesis or sterol efflux appear insensitive to dietary unsaturated fatty acids. The unsaturated fatty acid suppression of SREBP-1 and its targeted lipogenic genes is independent of LXRalpha

Selective proteolytic processing of rat hepatic sterol regulatory element binding protein-1 (SREBP-1) and SREBP-2 during postnatal development.

Sterol regulatory element-binding protein-1c (SREBP-1c) plays a major role in hepatic lipogenic gene expression. In adult animals, insulin and oxysterols induce SREBP-1c gene transcription, whereas polyunsaturated fatty acids suppress the nuclear content of SREBP-1c through pre-translational regulatory mechanisms. A decline in nuclear SREBP-1 is associated with suppression of hepatic lipogenesis. In contrast to adult rats, hepatic lipogenesis in preweaned neonatal rats is low. Ingestion of milk fat by the neonate may contribute to low hepatic lipogenesis. In this report, we tested the hypothesis that low lipogenic gene expression prior to weaning correlates with low mRNA(SREBP-1c), as well as low precursor and nuclear forms of SREBP-1. In contrast to expectations, levels of mRNA(SREBP-1c) and the 125-kDa SREBP-1 precursor in livers of preweaned rats was comparable with adult levels. Despite high levels of SREBP-1 precursor, mature (65 kDa) SREBP-1 was not detected in rat liver nuclei prior to 18 days postpartum. Weaning rats at 21 days postpartum was accompanied by a rise in nuclear SREBP-1 levels as well as increased lipogenic gene expression. In contrast, SREBP-2 was present in rat liver nuclei, and its target gene, HMG-CoA reductase, was expressed above adult levels prior to weaning. These studies indicate that, prior to weaning, SREBP-2 but not SREBP-1 is proteolytically processed to the mature form. As such, SREBP-2-regulated genes are active. Failure of SREBP-1 to be processed to the mature form <18 days postpartum correlates with low hepatic lipogenic gene expression. This mechanism differs from the hormonal and fatty acid-mediated pre-translational control of SREBP-1c in adult liver.